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Old 07-12-2010, 07:39 AM   #1
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Location: Sioux Falls, South Dakota
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Service Engine Light

I have a 1998 [COLOR=#0072bc! important][COLOR=#0072bc! important]Ford [COLOR=#0072bc! important]Super [/COLOR][COLOR=#0072bc! important]Duty[/COLOR][/COLOR][/COLOR] V-10, with 42,000 miles on it, in my motorhome. I had the SEL come on and checked the codes. The code showed PO-401 (EGR insufficant flow). After I checked it out and replaced the DPFE sensor, I reset the codes. I have discovered that when I drive on flat terrain I have no problems. When I drive in terrain with grades and hills, I get the code. Any ideas?

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Old 07-12-2010, 10:57 AM   #2
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When you go uphill you are pushing the engine harder and are losing vacuum,and this may cause the low flow sensor to alarm. You possibly have a small vacuum leak on your rig along with the the engine working harder will cause this.

Hope this helps. Joe

99 F-350 4X4 PSD pulling a 24' Nash travel trailer
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Old 07-26-2010, 09:25 PM   #3
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You can check the vacuum line to the EGR valve as well. It's possible it has cracked or softened to the point it collapses when it gets a lot of vacuum on it. The valve won't open all the way. I also had one Ranger with that code that had a wiring harness problem, but it was only that one.
Two wrongs don't make a right, but three rights make a left.

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Old 08-02-2010, 08:45 PM   #4
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Possibly it's the Mass Air Flow sensor - easy fix

Originally Posted by tmh462 View Post
You can check the vacuum line to the EGR valve as well. It's possible it has cracked or softened to the point it collapses when it gets a lot of vacuum on it. The valve won't open all the way. I also had one Ranger with that code that had a wiring harness problem, but it was only that one.
I just went through the same thing (service engine soon). My friend is a certified Ford mechanic and works at a Ford dealer daily (so he's up to speed on these things). On my V-10 (with 40K miles) it turned out to be a slightly dirty Mass Air Flow (MAF) sensor. Ours is a 1999 V-10 with a conical air filter... the MAF is the component next to it in the air filter housing. Just 4 bolts and the entire assembly comes off, then disco the electrical connection. Remove the MAP (it's about 4" by 4"). There are two very short, very tiny, wires visible... that's where the air flows and those are the sensors. One was just a little blackened, the other was shiney. He simply sprayed them with brake cleaner and reinstalled it. The problem is fixed. I just completed a 4,000 mile trip and the problem really is gone! Hope that helps... at least it's worth a try. It's rare that you actually need a new sensor (as per my friend).
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